Diagnostic and diagnosis method for central nervous abnormality and phenylketonuria

ABSTRACT

There is provided a diagnostic for central nervous abnormality, comprising a labeled transmitter substance of central nervous system or a labeled precursor of the transmitter substance, whose at least one of carbon atoms is substituted for a carbon isotope wherein the diagnostic is useful for diagnosing a central nervous abnormality (e.g. depression, Alzheimer&#39;s disease, schizophrenia, etc.) by applying it to a living body by oral administration or injection and examining a change in an amount of the carbon isotope in a breath of the living body.

This application is a 371 of PCT/JP96/02206 filed Aug. 6, 1996.

TECHNICAL FIELD

The present invention relates to a diagnostic comprising a labeledtransmitter substance of a central nervous system or a labeled precursorof the transmitter substance, whose a specific carbon atom is replacedby a carbon isotope, which is used for diagnosing a central nervousabnormality and phenylketonuria by measuring an amount of the carbonisotope in a breath of the living body to which the diagnosis has beenadministered, and a diagnosis method using the above diagnostic.

BACKGROUND ART

Heretofore, various morbidities with respect to a central nerve, such asdepression, Alzheimer's disease, schizophrenia, etc. have been generallyreferred to as a "central nervous abnormality". Various pharmacologicaland biological studies on this central nervous abnormality have beenmade, and the study on a novel drug for treating these diseases bynormalizing a metabolic change has also been made.

Phenylketonuria is a morbidity caused by dysbolism of phenylalanine.

However, the elucidation of the mechanism of pathopoiesis and metabolicchange have never been sufficiently conducted, and a method for simplyand precisely diagnosing these diseases has never been established.

DISCLOSURE OF THE INVENTION

It is an object of the present invention to provide a method for simplyand precisely diagnosing diseases which are generally referred to as acentral nervous abnormality and phenylketonuria, and a diagnosis usedfor diagnosing these diseases.

The present inventors have intensively studied so as to accomplish theabove object. As a result, it has been found that, when a drugcontaining, as an active ingredient, a labeled transmitter substance ofa central nervous system or a labeled precursor of the transmittersubstance, whose at least one carbon atom is substituted for a carbonisotope, is administered to a living body and then an amount of carbonisotope in a breath is measured, the amount of carbon isotope reflectsthe central nervous abnormality and, therefore, the above drug is usefulas a diagnostic for central nervous abnormality. Accordingly, when usingthis diagnostic, the central nervous abnormality can be simply, quicklyand very precisely diagnosed by a simple operation without accompanyinginvasion of a subject.

That is, according to the present invention, there is provided adiagnostic for diagnosing central nervous abnormality, comprising thelabeled transmitter substance of the central nervous system or a labeledprecursor of the transmitter substance, whose at least one carbon atomis substituted for the carbon isotope, wherein the diagnostic is usedfor diagnosing central nervous abnormality by applying the diagnostic toa living body due to oral administration or injection, and examining achange in the amount of the carbon isotope in a breath of the livingbody. Further, there is also provided a diagnosis method using thediagnostic mentioned above.

Phenylalanine, which is included in the transmitter substance of centralnervous system or its precursor, is related to phenylketonuria.Therefore, when a drug containing phenylalanine labeled with a carbonisotope at at least one of the 1-position, 2-position and 3-position ofthe side chain as an active ingredient is administered to a living bodyand then an amount of carbon isotope in a breath of the living body ismeasured, the amount of carbon isotope reflects the phenylketonuria.Therefore, the above drug is also useful as a diagnostic forphenylketonuria. Accordingly, when using this diagnostic, thephenylketonuria can be easily, quickly and very precisely diagnosed by asimple operation without accompanying invasion of a subject.

That is, according to the present invention, there are provided adiagnostic for phenylketonuria, comprising phenylalanine labeled with acarbon isotope at at least one of the 1-position, 2-position and3-position of the side chain as an active ingredient, wherein thediagnostic is used for diagnosing a phenylketonuria by applying thediagnostic to the living body by oral administration or injection, andexamining a change in an amount of the carbon isotope in a breath in aliving body, and a diagnosis method using the same.

The diagnosis method using the diagnostic of the present invention is amethod using the breath of the subject as a specimen. Therefore, themethod has an advantage that the specimen itself can be easily collectedwithout injuring the body in comparison with a conventional diagnosismethod using blood as the specimen, and that operations for diagnosis,such as preliminary pretreatment of the specimen are not required.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a graph illustrating a change in radioactivity of ¹⁴ CO₂ in abreath with time after administering ¹⁴ C-phenylalanine in the animalmodel of schizophrenia.

FIG. 2 is a graph illustrating a change in radioactivity of ¹⁴ CO₂ in abreath with time after administering ¹⁴ C-phenylalanine in the animalmodel of depression.

FIG. 3 is a graph illustrating a change in radioactivity of ¹⁴ CO₂ in abreath with time after administering ¹⁴ C-phenylalanine in the animalmodel of dementia.

BEST MODE FOR CARRYING OUT THE INVENTION

The diagnostic for diagnosing central nervous abnormality of the presentinvention contains a substance prepared by labeling a transmittersubstance of central nervous system or its precursor with a carbonisotope, as an active ingredient. The carbon isotope may be anon-radioactive carbon isotope such as ¹³ C or a radioactive carbonisotope such as ¹¹ C and ¹⁴ C. The labeling of the transmitter substanceor its precursor with these isotopes can be conducted according to anormal process, for example, process by Dellaria et al. Dellaria, J. F.,Santarsiero, B. D., Tetrahedron Lett., 29, 6078 (1988)!. Sometransmitter substances of central nervous system prepared by labelingwith these carbon isotope are commercially available. For example,phenylalanine labeled with ¹³ C at the I-position, 2-position or3-position of the side chain is commercially available from CIL Company.

The transmitter substance of central nervous system or its precursor,which is labeled with the above carbon isotope, is selected from thesubstance related to central nervous abnormality. Typical examplesthereof include catecholamine substance such as phenylalanine, tyrosine,dopa, dopamine, norepinephrine (noradrenalin) and epinephrine(adrenalin); serotonin substance such as tryptophan and5-hydroxyindoleacetic acid; histamine substance such as histidine;choline substance such as choline, phosphatidylcholine andacetylcholine; and amino acid such as glutamic acid, aspartic acid,γ-amino butyric acid, glycine and taurine.

In labeling the catecholamine substance and serotonin substance, atleast one of carbon atoms of the side chain substituted on the aromaticring or heterocycle may be replaced by the carbon isotope. In labelingthe choline substance, a N-methyl group or a carbon atom at 1-positionor 2-position of choline skeleton may be replaced by the carbon isotope.

The diagnostic of the present invention can be prepared according to aconventional process except for containing the above labeled transmittersubstance of central nervous system or a labeled precursor of thetransmitter substance as the active ingredient. For example, thediagnostic can be formed into a dosage form suitable for ingestion ofthe subject by using the labeled transmitter substance of centralnervous system or a labeled precursor of the transmitter substance incombination with a suitable liquid diluent or a solid carrier. Thedosage unit form may be the same form as that of a conventional drug orfood and drink.

More specific examples of the form of the drug include dosage unit formprepared by using normal diluents or excipients such as fillers,extenders, binders, moistening agents, disintegrators, surfactants,lubricants, etc. Typical examples thereof include tablets, pills,powders, solutions, suspensions, emulsions, granules, capsules,suppositories and injections (e.g. solutions, suspensions, etc.).

When shaping into the form of tablets, as the carrier for preparation,there can be used excipients such as lactose, sucrose, sodium chloride,glucose, urea, starch, calcium carbonate, kaolin, crystalline cellulose,silicic acid, potassium phosphate, etc.; binders such as water, ethanol,propanol, simple syrup, glucose solution, starch solution, gelatinsolution, carboxymethyl cellulose, hydroxypropyl cellulose, methylcellulose, polyvinyl pyrrolidone, etc.; disintegrators such ascarboxymethyl cellulose sodium, carboxymethyl cellulose calcium,low-substitution degree hydroxypropyl cellulose, dried starch, sodiumalginate, agar powder, laminaran powder, sodium bicarbonate, calciumcarbonate, etc.; surfactants such as polyoxyethylene sorbitan fatty acidester, sodium lauryl sulfate, monoglyceride stearate, etc.;disintegration inhibitors such as sucrose, stearin, cacao butter,hydrogenated oil, etc.; absorption accelerators such as quaternaryammonium base, sodium lauryl sulfate, etc.; humectants such as glycerin,starch, etc.; absorbents such as starch, lactose, kaolin, bentonite,colloidal silicic acid, etc.; and lubricants such as purified talc,stearate, borax, polyethylene glycol, etc. Furthermore, tablets can beoptionally formed into tablets subjected to normal tablet coating, suchas sugar coated tablets, gelatin coated tablets, enteric coated tablets,film coated tablets, or double tablets and multilayer tablets.

When shaping into the form of pills, as the carrier for preparation,there can be used excipients such as glucose, lactose, starch, cacaobutter, hardened vegetable oil, kaolin, talc, etc.; binders such as gumarabic, tragacanth powder, gelatin, ethanol, etc.; and disintegratorssuch as laminarane, agar, etc. When shaping into the form ofsuppositories, as the carrier for preparation, there can be usedpolyethylene glycol, cacao butter, higher alcohol, esters of higheralcohol, gelatin, semisynthetic glyceride, etc. Capsules are normallyprepared by mixing a compound as the active ingredient of the presentinvention with the above various carries for preparation and chargingthe resulting mixture into a hard capsule, a soft capsule, etc.according to a normal process.

When preparing the drug of the present invention as injections such assolution, emulsion, suspension, etc., it is preferred that the solution,emulsion and suspension are sterilized and are isotonic with blood. Whenshaping into the form of these solution, emulsion and suspension, as thediluent, there can be used water, ethyl alcohol, macrogol, propyleneglycol, ethoxylated isostearyl alcohol, polyoxylated isostearyl alcohol,polyoxyethylene sorbitan fatty acid esters, etc. In this case, sodiumchloride, glucose or glycerin may be contained in the drug of thepresent invention in the amount enough to prepare an isotonic solution,and normal solubilizing agents, buffering agents and soothing agents maybe added. If necessary, colorants, preservatives, perfumes, flavors,sweeteners and other drugs may also be contained in the drug of thepresent invention.

The amount of the above labeled transmitter substance or a labeledprecursor of the transmitter substance to be contained in the drug ofthe present invention is not specifically limited, and can beappropriately selected from a wide range. It is preferred that thesubstance is normally contained in the pharmaceutical preparation in anamount of about 10 to 300 mg.

The administration method of the drug is not specifically limited, andcan be selected according to various forms of preparation, age and sexof the patient, conditions of diseases and other conditions. Forexample, the tablet, pill, solution, suspension, emulsion, granule andcapsule are orally administered. The injection can be intravenouslyadministered as it is or after mixing with a normal fluid replacementsuch as glucose, amino acid, etc. If necessary, the injection can alsobe intramuscularly, intracutaneously, subcutaneously orintraperitoneally administered as it is. The suppository isintrarectally administered.

The dose of the preparation is appropriately selected according todirection for use, age and sex of the patient, conditions of diseasesand other conditions. The amount of the compound of the presentinvention as the active ingredient is preferably about 0.5 to 5mg/kg/day and the preparation can be preferably administered 1 to 4times per day. The dose of the isotope can be about 100 mg/60 kg of bodyweight.

The present invention also provide a method for diagnosing a centralnervous abnormality (e.g. depression, Alzheimer's disease,schizophrenia, etc.) by using the diagnostic of the present inventionthus obtained as described above.

This diagnosis method is carried out by previously administering thediagnostic of the present invention to the subject and measuring theamount of carbon isotope in the breath of the subject.

The amount of carbon isotope, for example, is obtainable by measuring aconcentration of carbon dioxide in the breath and examining aconcentration of carbon isotope in carbon dioxide, or by measuringradioactivity in the breath.

In the former method, about 250 ml of the breath is directly collectedin an aluminum bag at each time where 0, 30, 60, 90, 120, 150 and 180minutes have passed since the diagnostic of the present invention wasadministered, and then the breath collected is analyzed and theconcentration of carbon dioxide in the breath, particularlyconcentration of carbon dioxide containing no carbon isotope and that ofcarbon dioxide containing the carbon isotope are measured.

The measurement of the concentration of carbon dioxide can be conductedaccording to a conventional method. For example, the measurement of ¹³CO₂ can be conducted by a mass spectrometry using a conventional massspectrometer, more specifically, automatic gas isotope specific massspectrometer see "mass spectrometer controlled by microprocessor forcompletely automated purification and isotope analysis of CO₂ in thebreath", Biomedical Mass Spectrometry, Vol. 6, 350-355, (1979); G. W.Ewing, Instrumental Methods of Chemical Analysis, (4th edition, 1975)!.The desired measurement of ¹³ CO₂ can also be conducted by an infraredspectrometry using an infrared spectrophotometer and a nuclear magneticresonance spectrometery e.g. (1) see Japanese Patent Publication No.61-42219, (2) P. Klein et al., "Application of Stable Isotopies toPediatric Nutrient and Gastroenterology: Measurement of NutrientAbsorption and Digestion Using ¹³ C" Vol.4 Journal of PediatricGastroenterology and Nutrition 9-19 (1985), and (3) P. Klein et al.,"The Commercial Feasibility of ¹³ C Breath Tests" Vol. 11 AnalyticalChemistry Symposium Series 347-353 (1982)!. Furthermore, the measurementof ¹³ CO₂ can also be conducted by using a spectrometer on the basis ofa laser such as semiconductor laser analyzing device e.g. see JapaneseLaid-Open Patent Publication No. 5-142146!.

According to the above analyzing methods using various instruments, theconcentration of carbon dioxide in the breath can be measured, therebydetermining a ¹³ CO₂ /¹² CO₂ ratio.

The present inventors have found first that there is a significantdifference in an amount of ¹³ CO₂ and ¹³ CO₂ /¹² CO₂ ratio, which aredetermined as described above, between a patient suffering fromdepression, Alzheimer's disease or schizophrenia and a healthy personand, therefore, the above diseases can be diagnosed by using the amount(e.g., represented by concentration or ratio) of the carbon isotope asan index. That is, there have hitherto been reported some examples inthe patient suffering from depression, e.g. abnormality such as defectof phenylalaninehydroxylase metabolizing phenylalanine into tyrosine atthe liver, reduction in metabolic turnover of tyrosine (reduction inactivity of tyrosinetransaminase), etc. However, there has never beenreported an example of taking notice of a metabolic function ofphenylalanine due to the enzyme defect and diagnosing the abnormality bymeasuring the concentration of carbon dioxide containing the carbonisotope in the breath. Therefore, the fact that depression can be easilyand simply diagnosed with high precision and high sensitivity by such abreath diagnosis method is a novel knowledge which has been found fistby the present inventors.

According to the breath diagnosis method using the diagnostic of thepresent invention, dementia (e.g. Alzheimer's disease, etc.) andschizophrenia, wherein an effective diagnosis method has never beenfound heretofore, can also be easily and simply diagnosed with highprecision according to the same mechanism as that described above.

Phenylketonuria is broken out by accumulation of phenylalanine in bloodor brain without being metabolized. Therefore, according to the methodfor measuring the breath using the diagnostic comprising phenylalaninelabeled with a carbon isotope at at least one of the 1-position,2-position and 3-position of the side chain as an active ingredient ofthe present invention, the patient suffering from phenylketonuria can beeasily and simply diagnosed with high precision according to the samemechanism as that described above.

INDUSTRIAL APPLICATION

As described above, the present invention provides a novel technique fordiagnosing central nervous abnormality and phenylketonuria, and thevalue of the present invention in the clinical diagnosis is great.

EXAMPLES

The following Test Examples and Examples further illustrate the presentinvention in detail.

Test Example 1

(Test due to an animal model of schizophrenia)

It was examined whether a metabolism of ¹⁴ C-phenylalanine administeredorally changes or not by comparing an animal model of schizophrenia witha normal animal, using an amount of ¹⁴ CO₂ excreted in a breath as anindex.

The animal model of schizophrenia means that in which a stereotypedbehavior (e.g. behavior of continuous sniffing, licking, etc.) isdeveloped in an animal by administering Apomorphine. Apomorphine has anagonist action to a dopamine receptor and has frequently been used so asto develop a remedy for schizophrenia, heretofore C. J. E. Niemegeereset al., Arch. int. Pharmacodyn. 227, 238-253 (1977) and A. J. Puech etal., Neuropharmacol. 20, 1279-1284 (1981)!.

The test was conducted as follows.

Animal used: Wistar strain male rat (body weight: 250-270 g)

Drug used: ¹⁴ C-phenylalanine (L-phenyl 1-¹⁴ C!alanine, manufactured byAmrersham Life Science Co.) apomorphine hydrochloride (manufactured bySigma Chemical Co., Ltd.)

Test method:

The total examples of the test group were six, i.e. the apomorphineadministration group of three examples and control group of threeexamples. ¹⁴ C-Phenylalanine (1.5 ml) having a concentration of 1.85MBq/ml was diluted with distilled water (6 ml) in a fivefold dilution toprepare a solution having a concentration of 0.37 MBq/ml. The resultingsolution was orally administered to individuals with a volume of 1 mlper individual rat.

Apomorphine (10 mg) was dissolved in saline to prepare a solution havinga concentration of 2 mg/ml. The resulting solution was subcutaneouslyadministered with a volume of 1 ml per individual rat of the apomorphineadministration group. On the other hand, only saline was subcutaneouslyadministered to the control group with the same volume as that describedabove.

An amount of ¹⁴ CO₂ derived from the metabolized ¹⁴ C-phenylalanine inthe breath was determined by trapping the breath in a breath trappingsolvent (a mixture wherein 2-aminoethanol and methanol are mixed at 1:3)installed in a metabolism testing device, collecting 1 ml of thissolvent in a scintillation vial every fixed time, diluting the solventwith a scintillation cocktail solution (10 ml) and counting aradioactivity with a liquid scintillation counter for β ray.

In the test, each rat was firstly put in a metabolism testing deviceand, 15 minutes after standing, a breath trapping solvent was collectedand a radioactivity was measured. The resulting radioactivity was takenas a value immediately before administration. Immediately aftercollecting the breath trapping solvent for measuring thisvalue-before-administration, apomorphine and ¹⁴ C-phenylalanine weresimultaneously administered to rats of the apomorphine administrationgroup. Then, the breath trapping solvent was collected four times every15 minutes until 60 minutes have passed since administration, and theradioactivity was measured. A value obtained by subtracting the previousvalue from the resulting radioactivity count (dpm) was statisticallytreated as a data every predetermined time. Saline of the same volume asthat of the above apomorphine solution and ¹⁴ C-phenylalanine weresimultaneously administered to rats of the control group.

In the statistical treatment, an average and a standard error of dataobtained every each group and each collecting time were determined andsubjected to a dispersion analysis on the basis of the repeatedmeasurement, and then a difference between groups was statisticallyassumed.

The test results are shown in FIG. 1. As is apparent from FIG. 1, in theapomorphine administration group, ¹⁴ CO₂ in the breath was low in allmeasured points after administration of ¹⁴ C-phenylalanine in comparisonwith the control group wherein no apomorphine was administered. At 30minutes after administration, the difference was statisticallysignificant. That is, it has been confirmed by Dunnett's two-tailed testthat there is a significant difference between the apomorphine group andcontrol group in a probability of 5%.

Therefore, it has been found that the measurement of the amount of ¹⁴CO₂ in the breath makes it possible to assume the fact that a metabolicrate of phenylalanine is decreased.

Test Example 2

(Test due to animal model of depression)

It was examined whether a metabolism of ¹⁴ C-phenylalanine administeredorally changes or not by comparing an animal model of depression with anormal animal, using an amount of ⁴ CO₂ excreted in a breath as anindex.

It is assumed that depression is caused by depression of monoamine nervetransmission in the brain. Since reserpine has a strong monoaminedepletion action, symptoms similar to those of depression (e.g.inhibition of spontaneous behavior, reduction in body temperature,lethargy, etc.) is developed when this drug is administered to theanimal. Therefore, it has hitherto been used as the animal model ofdepression Howard, J. L. et al., : Antidepressants: Neurochemical,behavioral, and clinical perspectives (ed. by Enna, S. J., Malick, J. B.and Richelson, E.), 107-120, Raven Press, New York, 1981!.

The test was conducted as follows.

Animal used: Wistar strain male rat (body weight: 250-270 g)

Drug used: ¹⁴ C-phenylalanine (L-phenyl 1-¹⁴ C!alanine, manufactured byAmersham Life Science Co.)

Reserpine (Apoplon Inj., 1 mg/ml, manufactured by Daiichi Seiyaku Co.,Ltd.)

Test method:

The total examples of the test group were six, i.e. the reserpineadministration group of three examples and control group of threeexamples. ¹⁴ C-phenylalanine (1.5 ml) having a concentration of 1.85MBq/ml was diluted with distilled water (6 ml) in a fivefold dilution toprepare a solution having a concentration of 0.37 MBq/ml. The resultingsolution was orally administered to individuals with a volume of 1 mlper individual rat.

Reserpine was subcutaneously administered with a volume of 1 ml/kg perindividual rat of the reserpine administration group. Since 16 to 18hours are required for reserpine to develop the effect, after 18 hoursfrom administration of reserpine, ¹⁴ C-phenylalanine was administratedto rats.

On the other hand, only saline was subcutaneously administered to ratsof the control group with the same volume as that of reserpine at thesame time as that of administration of reserpine.

An amount of ¹⁴ CO₂ derived from the metabolized ¹⁴ C-phenylalanine inthe breath was determined by counting a radioactivity according to thesame manner as that described in Test Example 1.

In the test, each rat was firstly put in a metabolism testing deviceand, at 15 minutes after standing, a breath trapping solvent wascollected and a radioactivity was measured. The resulting radioactivitywas taken as a value immediately before administration. Immediatelyafter collecting the breath trapping solvent for measuring thisvalue-before-administration, ¹⁴ C-phenylalanine was administered torats. Then, the breath trapping solvent was collected four times every15 minutes until 60 minutes have passed since administration, and theradioactivity was measured. A value obtained by subtracting the previousvalue from the resulting radioactivity count (dpm) was statisticallytreated as a data every time.

In the statistical treatment, an average and a standard error of dataobtained every each group and each collecting time were determined andsubjected to a dispersion analysis on the basis of the repeatedmeasurement, and then a difference between groups was statisticallyassumed.

The test results are shown in FIG. 2. As is apparent from FIG. 2, in thereserpine administration group, an amount of ¹⁴ CO₂ in the breath washigh in all measured points after administration of ¹⁴ C-phenylalaninein comparison with the control group wherein no reserpine wasadministered, and the difference was statistically significant. That is,it has been confirmed by Dunnett's two-tailed test that there is asignificant difference between the reserpine group and control group ina probability of 0.1%.

Test Example 3

(Test due to animal model of dementia)

It was examined whether a metabolism of ¹⁴ C-phenylalanine administeredorally changes or not by comparing an animal model of dementia with anormal animal, using an amount of ¹⁴ CO₂ excreted in a breath as anindex.

It is considered that memory disorder and intellectual functiondisorder, which are identified as a main symptom of dementia, are causedby depression of neuronal activity of acetylcholine ordegeneration/deciduation of nerve cells.

Scopolamine is an antagonist of muscarinic acetylcholine M1 receptor,and has an action of blocking an acetylcholinenerve transmission whenincorporated into a central nervous system by peripheral administration.This action can easily cause memory/learning disorder in the animal.Therefore, scopolamine has widely been used for a study on dementia as adrug of developing main mobility of dementia, heretofore Matsuoka N, etal, J. Pharmacol. Exp. Ther. 263 (2), 436-444 (1992), and Davis, L., etal, J. Med. Chem. 39 (2), 582-587 (1996)!.

The test was conducted as follows.

Animal used: Wistar strain male rat (body weight: 250-270 g)

Drug used: ¹⁴ C-phenylalanine (L-phenyl 1-¹⁴ C!alanine, manufactured byAmerican Radiolabeled Chemicals Inc.)

Scopolamine hydrobromide (manufactured by Sigma Chemical Co., Ltd.)

Test method:

The total examples of the test group were six, i.e. the scopolamineadministration group of three examples and control group of threeexamples. ¹⁴ C-phenylalanine (0.75 ml) having a concentration of 3.7MBq/ml was diluted with distilled water (6.75 ml) in tenfold dilution toprepare a solution having a concentration of 0.37 MBq/ml. The resultingsolution was orally administered to individuals with a volume of 1 mlper individual rat.

Scopolamine (1 mg) was dissolved in saline (1 ml) and the resultingsolution was injected to the rat intraperitonealy with a volume of 1ml/kg. In the control group, only saline was injected to the ratintraperitonealy with the same volume as that of scopolamine.

An amount of ¹⁴ CO₂ derived from the metabolized ¹⁴ C-phenylalanine inthe breath was determined by counting a radioactivity according to thesame manner as that described in Test Example 1.

In the test, each rat was firstly put in a metabolism testing deviceand, 15 minutes after standing, a breath trapping solvent was collectedand a radioactivity was measured. The resulting radioactivity was takenas a value immediately before administration. Immediately aftercollecting the breath trapping solvent for measuring thisvalue-before-administration, ¹⁴ C-phenylalanine was administered torats. Then, the breath trapping solvent was collected four times every15 minutes until 60 minutes have passed since administration, and theradioactivity was measured. A value obtained by subtracting the previousvalue from the resulting radioactivity count (dpm) was statisticallytreated as a data every time.

In the statistical treatment, an average and a standard error of dataobtained every each group and each collecting time were determined andsubjected to a dispersion analysis on the basis of the repeatedmeasurement, and then a difference in group was statistically assumed.

The test results are shown in FIG. 3. As is apparent from FIG. 3, in thescopolamine administration group, an amount of ¹⁴ CO₂ in the breath waslow at all measured points after administration of ¹⁴ C-phenylalanine incomparison with the control group wherein no scopolamine wasadministered, and the difference was statistically significant.

Example 1

Phenylalanine labeled with ARC at the 1-position (manufactured byGoseihin Co. Ltd.) was administered to a patient suffering fromdepression and a normal person with a dose of 100 mg/body. At 0, 30, 60,90, 120, 150 and 180 minutes after administration, a breath (250 ml) wascollected in an aluminum bag and a concentration ratio of ¹² CO₂ to ¹³CO₂ was measured by using a mass spectrometer (manufactured by FinigunMat Instrument Inc; Breathmat Co.), thereby diagnosing with the measuredconcentration ratio.

As a result, it has become apparent that depression can be preciselydiagnosed according to the diagnosis process using the diagnostic of thepresent invention.

The reason is that, regarding the patient suffering from depression, anactivity of a metabolic enzyme of phenylalanine is lowered at the liverand therefore a metabolism to tyrosine is delayed.

Examples 2 and 3

According to the same manner as that described in Example 1,phenylalanine labeled with ¹³ C at the 1-position (manufactured byGoseihin Co. Ltd.) was administered to patients suffering fromAlzheimer's disease and schizophrenia in place of the patient sufferingfrom depression, and a normal person with a dose of 100 mg/body. At 0,30, 60, 90, 120, 150 and 180 minutes after administration, a breath (250ml) was collected in an aluminum bag and a concentration ratio of ¹² CO₂to ¹³ CO₂ was measured by using a mass spectrometer (manufactured byFinigun Mat Instrument Inc; Breathmat Co.), thereby diagnosing with themeasured concentration ratio.

As a result, it has become apparent that Alzheimer's disease andschizophrenia can be precisely diagnosed according to the diagnosisprocess using the diagnostic of the present invention.

We claim:
 1. A diagnostic for a central nervous system abnormality,comprising a labeled transmitter substance of the central nervous systemor a labeled precursor of said transmitter substance, having at leastone carbon atom substituted by a carbon isotope, and upon beingadministered to a living animal by oral administration or injection,functions to diagnose the central nervous system abnormality due to achange in an amount of the carbon isotope contained in the breath of theliving animal, wherein said labeled transmitter substance of the centralnervous system or its labeled precursor is at least5-hydroxyindoleacetic acid, a histamine substance, a choline substanceor a catecholamine substance, wherein said catecholamine substance is atyrosine, a dopa, a dopamine, a norepinephrine or an epinephrine.
 2. Thediagnostic according to claim 1, wherein the histamine substance is ahistidine.
 3. The diagnostic according to claim 1, wherein the cholinesubstance is a choline, a phosphatidylcholine or an acetylcholine. 4.The diagnostic according to claim 1, wherein the carbon isotope used forlabeling is radioactive or non-radioactive.
 5. The diagnostic accordingto claim 1, wherein the central nervous system abnormality isdepression, dementia or schizophrenia.
 6. A composition to be used as adiagnostic for a central nervous system abnormality, comprising adiagnostically effective amount of a labeled transmitter substance ofthe central nervous system or a labeled precursor of said transmittersubstance, having at least one carbon atom substituted by a carbonisotope, and a pharmaceutically available carrier, wherein said labeledtransmitter substance of the central nervous system or its labeledprecursor is at least 5-hydroxyindoleacetic acid, a histamine substance,a choline substance or a catecholamine substance, wherein saidcatecholamine substance is a tyrosine, a dopa, a dopamine, anorepinephrine or an epinephrine.
 7. A method for diagnosing a centralnervous system abnormality, which comprise administering a diagnosticfor a central nervous system abnormality to a living animal by oraladministration or injection, and examining a change in an amount of acarbon isotope in the breath of the living animal, by comparing saidamount of carbon isotope in the breath of said living animal to theamount of carbon isotope in the breath of the same species of livinganimal that does not have a central nervous system abnormality, whereinthe diagnostic comprises a labeled transmitter substance of the centralnervous system or a labeled precursor of said transmitter substance,having at least one carbon atom substituted by the carbon isotope.
 8. Amethod according to claim 7, wherein the amount of the carbon isotope isrepresented by the ratio of an amount of carbon dioxide which is labeledwith a carbon isotope in the breath of the living animal, to that ofcarbon dioxide which is not labeled with the carbon isotope.
 9. A methodaccording to claim 7, wherein the amount of the carbon isotope isrepresented by the radioactivity of the breath of the living animal. 10.A method according to claim 7, wherein the transmitter substance of thecentral nervous system or its precursor is a catecholamine substance, aserotonin substance, a histamine substance or a choline substance.
 11. Amethod according to claim 7, wherein the transmitter substance of thecentral nervous system or its precursor is of 5-hyxdroxyindoleaceticacid, a histamine substance, a choline substance or catecholeaminesubstance wherein said catecholeamine substance is a tyrosine, a dopa, adopamine, a norepinephrine or an epinephrine.
 12. A method according toclaim 7, wherein the central nervous system abnormality is dementia. 13.A method according to claim 7, wherein the central nervous systemabnormality is depression.
 14. A method according to claim 7 wherein thecentral nervous system abnormality is Alzheimer's disease.
 15. A methodaccording to claim 7,wherein the central nervous system abnormality isschizophrenia.